Electrophotographic element of azo dye layer and charge transport overlayer

ABSTRACT

The present invention relates to an electrophotographic recording material consisting of an electroconductive support material with a photoconductive double layer of organic materials which consists of a homogeneous, opaque, charge carrier producing dyestuff layer and a transparent top layer of insulating materials containing at least one charge transporting compound, which is characterized in that the organic dyestuff layer consists of a compound of the general formula   WHEREIN -A- is a diphenyl, 2-phenyl-benzimidazole or azobenzene group which may be substituted, and R, R1, R2 and R3 may be the same or different and are hydrogen, alkyl with one to four carbon atoms, alkoxyl with one to four carbon atoms, or halogen.

United States Patent 1191 Rochlitz 1 1 ELECTROPHOTOGRAPHIC ELEMENT OF AZO DYE LAYER AND CHARGE TRANSPORT OVERLAYER [75] Inventor: Jiirgen Rochlitz, Breckenheim,

Germany [73] Assignee: Hoechst Aktiengesellschaft, Germany [22] Filed: Apr. 25, 1973 [21] Appl. No.: 354,319

[30] Foreign Application Priority Data Sept. 21, 1972 Germany 2226254 52 us. (:1. 96/1.6; 96/l.5; 252/501 51 1111.0 ..G03g 5/06 [58] Field of Search 96/1 R, 1 PE, 1.3, 1.5,

[56] References Cited UNITED STATES PATENTS 3,287,123 11/1966 Hoegl 96/1.5 3,384,488 5/1968 Tulagin et a1 96/1 .3 X 3,549,358 12/1970 Clecak et al..... 96/l.5 X 3,591,374 7/1971 Seus 96/1.6

3,598,582 8/1971 Herrick et a1 96/l.5 3,634,079 1/1972 Champ et a1. 96/l.6 X 3,658,675 4/1972 Jones 96/l.3 X

3,681,064 8/1972 Yeh 96/1 PE 3,684,548 8/1972 Contois 96/1.6 X

3,725,058 4/1973 Hayashi et al. 96/1.5

FOREIGN PATENTS OR APPLICATIONS OTHER PUBLICATIONS Chadwell et al., Photoconductor, IBM Tech. Discl. Bull., Vol. 14, No. 9, Feb. 1972, p. 2781.

1 1 May 20, 1975 Primary ExaminerRoland E. Martin, Jr. Attorney, Agent, or FirmJames E. Bryan [57] ABSTRACT The present invention relates to an electrophotographic recording material consisting of an electroconductive support material with a photoconductive double layer of organic materials which consists of a homogeneous, opaque, charge carrier producing dyestuff layer and a transparent top layer of insulating materials containing at least one charge transporting compound, which is characterized in that the organic dyestuff layer consists of a compound of the general formula A is a diphenyl, 2-phenyl-benzimidazole or azobenzene group which may be substituted, and R, R R and R may be the same or different and are hydrogen, alkyl with one to four carbon atoms, alkoxyl with one to four carbon atoms, or;

halogen.

19 Claims, 2 Drawing Figures ENTEB HAYZO iEUS SHEET 10F 2 Fig.2

ELECTROPHOTOGRAPHIC ELEMENT OF AZO DYE LAYER AND CHARGE TRANSPORT I OVERLAYER 2 This invention relates to an electrophtographic re- -5 cording material consisting of an electroconductive support material and a photoconductive double layer of organic materials which consists of a homogeneous, opaque, charge carrier producing dyestuff layer and of a transparent top layer of insulating materials containing at least one charge transporting compound.

It is known from German Offenlegungsschriften Nos. 1,597,877 and 1,797,342 for electrophotographic recording material to extend the spectral sensitivity of selenium layers to the red spectral range by a double layer arrangement, e.g. with phthalocyanine dispersion layers. Disadvantageous are the vacuum vapor depositions of selenium requiring high technical expenditure, the brittleness of comparatively thick selenium layers,

the poor adhesion of adjacent heterogeneous constituents in these layers and the only difficultly realizable uniformly wetting coating with the corresponding dispersions. Furthermore, no optimum light-sensitivities can be achieved as a result of the absorption behavior and the different charge conducting mechanisms of selenium and phthalocyanine in the double layer arrangement.

From U.S. Pat. No. 3,573,906, for example, there are also known photoconductive double layers containing an organic, possibly photoconductive, insulating layer bly diluted homogeneous solution of a sensitizer in a binder is provided with an upper transparent lightsensitive layer. This layer construction, however, only offers a relatively low sensitivity increase only little meeting technical demands. Another known suggestion according to German Offenlegungsschrift No. 1,909,742 is to repeatedly pour a sensitizer solution over a photoconductive layer and to evaporate the solvent. A disadvantage thereof is the low mechanical resistance of the applied layer as a result of insufficient cohesion and adhesion of the applied sensitizer. Furthermore, repeated coating is cumbersome.

The construction of photoconductive double layers containing a dyestuff layer is also known, e.g. from Belgian Pat. Nos. 763,389 and 763,541, but for this layer construction, top layers are used which allow no sensitivities satisfying highest demands and, as regards adhesion between the dyestuff layer and the top layer, do not represent an optimization and are not sufficiently resistant to mechanical attack, e.g. in electrophotographic copying devices, particularly to that due to the cleaning of .the photoconductive layer.

It is the object of the present invention to provide an organic photoconductor layer highly light-sensitive for the xerographic copying procedure which overcomes I the described disadvantages and the adhesion of which between the various layers satisfies the highest technical demands, which exhibits substantially no wear or fatigue and which, even after repeated use, may be used again rapidly.

The present invention provides an electrophotographic recording material consisting of an electroconductive support material with a photoconductive double layer of organic materials which consists of a homogeneous, opaque, charge carrier producing dyestuff layer and a transparent top layer of insulating materials containing at least one charge transporting compound, which is characterized in that the organic dyestuff layer consists of a compound of the general formula light in the visible range of the spectrum. According to German Offenlegungsschrift No. 2,120,912, it has also been suggested to use those light-sensitive layer arrangements for electrophotographic recording materials which contain, as the charge carrier producing layer, an inorganic material, such as the sulfide, selenide, sulfoselenide or telluride of cadmium or zinc,

and, as the charge carrier transporting layer, an organic material with at least 20 per cent by weight of 2,4,7-trinitro-9-fluorenone. A disadvantage of the production of these layers with inorganic photoconductors is the exact observation of the vapor deposition conditions of selenium or the exact adjustment of the mixtures in order to obtain a good photoconductive modificationof the inorganic materials. Furthermore, the adhesion of selenium to conductive support material, such as to aluminium, is insufficient. Fatigue in repeated charge/exposure cycles does not allow the use wherein A is a diphenyl, 2-phenyl-benzimidazole or ambenzene group which may be substituted, and

R, R R and R may be the same or different and are hydrogen, alkyl with one to four carbon atoms, alkoxyl with one to four carbon atoms, or halogen and that the transparent top layer consists of a mixture of a binder with a charge transporting, monomer, heterocyclic compound substituted by at least one dialkyl amino group or two alkoxy groups and having an extended Ir-electron system or with a condensation product of 3-bromo-pyrene and formaldehyde.

By means of the invention, it is possible to obtain highly light-sensitive, photoconductive double layers for the electrophotographic recording material of the invention which have a high mechanical resistance and may be arranged on a cylindrical drum, for example, or may circulate as an endless belt without exhibiting special signs of wear and thus are very suitable for the use in electrophotographic copying devices. The high lightsensitivity particularly results from the fact that the charge transporting compound present in the transparent top layer is sensitized by the charge carrier producing dyestuff layer in that the charge carriers, i.e., electrons or holes, are taken up by the top layer.

In a preferred embodiment, the organic dyestuff layer has a thickness in the range from about 0.005 to about 2 am, preferably from about 0.01 to about 2 pm. A high concentration of excited dyestuff molecules is achieved thereby in the dyestuff layer and at the boundary surface between the dyestuff layer and the top layer. Furthermore, the adhesion between the electroconductive support material and the top layer is not impaired.

In a preferred embodiment, the transparent top layer has a thickness in the range from about to about 20 pm. This assures a sufficiently high charge acceptance.

The structure of the electrophotographic recording material according to the invention is shown in the attached FIGURES.

FIG. 1 shows a material consisting of an electroconductive support 1, an organic dyestuff layer 2, and an organic transparent top layer 3.

FIG. 2 shows a metallized plastic layer 1,4 as the support, to which an intermediate layer 5 is applied which prevents the injection of charge carriers in the dark. This combination is coated with a photoconductive double layer consisting of the organic dyestuff layer 2 and an organic, transparent top layer 3.

Suitable electroconductive support materials 1 or 1,4, respectively, are materials that have been hitherto used for this purpose, in particular metal foils, such as aluminum thin or lead foils, or supports of possibly transparent plastic materials to which a layer of the above metals has been applied by lamination or vapor deposition. The intermediate layer 5 shown in FIG. 2 consists of an organic material, e.g. a polyamide resin, or of a metal oxide layer, e.g. an aluminum oxide layer, produced by a thrermal, anodic or chemical process.

The organic dyestuff layer of the electrophotographic material substantially determines the spectral light-sensitivity of the photoconductive double layer of the invention.

In the following table, a number of suitable dyestuffs are listed which correspond to the general formula above, wherein the diphenyl, 2-phenyl-benzimidazole or azobenzene groups preferably are substituted by alkyl with one to four carbon atoms, alkoxyl with one to four carbon atoms, and/or halogen, especially chlorme:

Formula Name of the Dyestuff Identification 1 Pigment Yellow 12 CI. 21,090 2 Pigment Orange 16 CI. 21,160 3 Pigment Yellow 17 Cl. 21.105 4 Vulcanechtgelb" GR C.l. 21,100 5 Pigment Orange 15 CI. 21,130 6 Vulcanechtgelb" R C.I. 21,135 7 Vulcanechtgelb" 5 G C.I. 21,220 8 Vulcanechtgelb" G C.I. 21,095 9 Vulcanechtorange GG C.I. 21,165 10 Pigment Yellow 63 C1. 21,091 1 l Pigment Yellow 55 C1. 21,096 12 Helio Brilliant Yellow GR C.l. 20,045 13 Permanent Yellow NGG C.l. 20,040 14 Bis-4,6-(acetoacetanilidofi-azo)- C.I. 21,160

Z-phenyl-benzimidazole, prepared analogously to 15 4,4 -bis'azo-( 2,5-dichloro-2'- methoxy-S '-methyl-azobenzene bis-(B-acetoacetanilide) l6 4,4-bis-a7.o-( 2,5 '-dichloro-5 ,2-

dimethoxyazobenzene )-bis-( [3- acetoacetanilide) v Of these dyestuffs, those numbered 1, 2, l5, and 16 have proved to be particularly advantageous.

The tn'sazodyestuffs Nos. 15 and 16 are prepared according to the following process, which is described with reference to the dyestuff No. 16 but may also be used for the dyestuff No. 15 when using the appropriate starting materials:

34 parts by weight of 4,4'-diamino-2,5-dichloro- 5,2-dimethoxy-azobenzene are mixed for about 1 hour with 250 parts by volume of glacial acetic acid and parts by volume of Sn hydrochloric acid. Diazotization is performed at a temperature between 0 and 5 C, using 41 parts by volume of Sn sodium nitrite solution, and excess nitrite is destroyed after 1 hour by adding amido sulfonic acid.

In a second vessel, 35 parts by weight of acetoacetanilide are mixed with 500 parts by volume of water and dissolved by adding parts by volume of 2n caustic soda solution to the mixture.

The cleared alkaline solution of the coupling component is then added, dropwise, to the solution of the diazonium salt at a temperature between 5 and 10 C. After termination of the coupling process, the dyestuff suspension is heated for 1 hour to 90 C. The brown product is drawn off by suction, washedd with water, again suspended in 500 parts by volume of hot alcohol, drawn off again, and finally dried at 60 to 70 C. The resulting dyestuff is of the structure of Formula 16 and may be used for the present invention.

The organic dyestuff layer must be extremely uniform since only its uniformity guarantees a uniform injection of charge carriers into the top layer. To achieve this object, the dyestuff layers are applied according to special coating methods. Such methods are the application by mechanically rubbing the most finely powdered dyestuff material into the electroconductive support material, the application by chemical deposition of a leucobase to be oxidized, for example, the application by electrolytical or electrochemical processes or the gun spray method. The application preferably is performed, however, by vapor depositing the dyestuff in the vacuum. A tightly packed homogeneous coating is achieved thereby.

The tightly packed coating makes it unnecessary to produce thick dyestuff layers for achieving a high absorption. The tightly packed dyestuff molecules and the extremely low layer thickness permit, in a particularly advantageous manner, the transport of charge carriers so that it is completely sufficient to produce the charge carriers at the boundary layer only.

Excitation (l) and charge separation (2) take place in the dyestuff layer according to the following reaction equations:

1. S hv S 2. S S 8 '8 with S dyestuff molecule S' excited dyestuff molecule, and

-S -S dyestuff radical ions.

At the boundary surface between the organic dyestuff layer and the transparent top layer, reactions of the excited dyestuff molecules or the resulting charge carriers in the form of the dyestuff radical ions with the molecules of the charge transport effecting compound in the top layer are possible according to the following equations:

F donor molecule F acceptor molecule -F -F --donor or acceptor-radical ion.

At the boundary surface, sensitizing reactions take place between the transparent top layer and the organic dyestuff layer. The top layer thus is a sensitized organic photoconductor at least in the area of the boundary surface, which leads to the surprisingly high photoconductivity.

Reactions 3 and 5 proceed preferably when the ar-electron system in the top layer is a compound which, as a donor compound, easily can release electrons. This is the case with 2,5-bis-(4-diethylaminophenyl)-l ,3,4-oxadiazole, for example. Reactions 4 and 6 are preferably possible with a substance in the top layer which, as an electron acceptor, easily accepts electrons, e.g. 2,4,7-trinitrofluorenone or N-t-butyl- 3,6dinitro-naphthalimide.

Due to the characteristic features of the invention it is sufficient for the efficiency of the dyestuff when, besides its intense absorption, it only has either electronattracting substituents, e.g. C O, NO halogen, or electron-repelling substituents, e.g. Nl-l N-alkyl or Oalkyl, depending on whether it is preferably suitable for reactions 3,5 or 4,6. The invention permits charge carrier transport fostered by a particularly low expenditure of energy within the tightly packed dyestuff layer according to the following reactions: A

In all conventional sensitizing processes, however, transport via the dyestuff molecules present in low concentration is impeded by their large distance from one another.

Analogous is the procedure of the charge transport in the top layer with:

9. "F F F, 7 (p-conductive) 10. F F F F (n-conductive).

The practical consequence of reactions 1 to 10 is that, in the use of electron donors in the top layer, the

If it is to be negatively charged, the transparent top layer preferably consists of a mixture of an electron donor compound and a binder. but when the electrophotographic recording material is to be used for positive charging the transparent top layer consists of a mixture of an electron acceptor compound and a binder.

Consequently, in the transparent top layer there are used compounds for charge transport which are known as electron donors or electron acceptors. They are used together with binders or adhesives adapted to the compound for charge transport as regards charge transport, film property, adhesion, and surface characteristics. Furthermore, conventional sensitizers or substances forming charge transfer complexes may be present. But they can only be used in so far as the necessary transparency of the top layer is not impaired. Finally, other usual additives such as levelling agents, plasticizers, and adhesives may'also be present.

Suitable compounds for charge transport are especially those organic compounds which have an extended rr-electron system, e.g. monomer aromatic heterocyclic compounds.

Monomers employed in accordance with the invention are those which have at least one substituted I amino group or two alkoxy groups. Particularly proved double layer arrangement is negatively charged so that reactions 3,5,8,9 can proceed. In the inverse case, layers with electron acceptors in the top layer are positively charged so that reactions 4,6,7, and 10 can proceed.

As already mentioned, the dyestuff layers are very thin so that only very little dyustuff is used. Application by vapor deposition in a high vacuum assures an extremely high uniformity of the dyestuff layer, however, such as can not normally be achieved by conventional coating methods. This uniformity contributes largely to the high light-sensitivity which distinguishes the layers according to the invention, the fact that the charge transport reactions 3 to 6 can proceed without locally disturbing each other (re-combinations) being a further advantage.

The transparent top layer has a high electric resistance and prevents in the dark the flowing off of the electrostatic charge. Upon exposure to light, it transports the charges produced in the organic dyestuff layer.

have heterocyclic compounds, such as the oxadiazole derivatives, mentioned in German Pat. No. 1,058,836. An example thereof is in particular the 2,5-bis-(4-diethylaminophenyl)-oxadiazole-l,3,4. Further suitable monomer electron donor compounds are, for example, triphenyl amine derivatives, benzo-condensed heterocycles, pyrazoline or imidazole derivatives, as well as triazole and oxazole derivatives, as disclosed in German Pat. Nos. 1,060,260 and 1,120,875, or carbocyclic compounds.

Formaldehyde condensates of various aromatic compounds, e.g. the formaldehyde condensates of 3- bromopyrene, may also be used.

Besides these mentioned compounds having predominantly a p-conductive character, it is also possible to use n-conductive compounds. These so-called electron acceptors are known from German Pat. No. 1,127,218, for example. Compounds such as 2,4,7- trinitrofluorenone or N-t-butyl-3 ,6-dintronaphthalimide have proved particularly suitable.

Suitable binders with regard to flexibility, film properties, and adhesion are natural and synthetic resins. Examples thereof are in particular polyester resins, e.g. those marketed under the names Dynapol (Dynamit Nobel), Vitel (Goodyear), which are copolyesters of isoand terephthalic acid with glycol. Silicone resins as those known under the names SR of General Electric Comp. or Dow 804 of Dow Corning Corp., U.S.A., and which are three-dimensionally cross-linked phenylmethyl siloxanes or the so-called reactive resins, e.g. the so-called DD lacquers consisting of an equivalent mixture of polyesters or polyethers containing hydroxyl groups and polyfunctional isocyanates, e.g. of the Desmophen or Desmodur type marketed by Bayer AG, Leverkusen, Germany, have proved particularly suitable. Furthermore, copolymers of styrene and maleic acid anhydride, e.g. those known under the name Lytron, Monsanto, and polycarbonate resins, e.g. the resins known by the name of Lexan Grade of General Electric, U.S.A. may be used. Further, afterchlorinated polyvinyl chlorides, such as Rhenoflex (a product of Dynamit Nobel AG-., Troisdorf, Germany), and chlorinated polypropylene, such as Hostaflex (a product of Farbwerke Hoechst AG, Frankfurt/M., Germany) are also 'very suitable.- i

The mixing ratio of charge transporting compound to binder may vary. Relatively certain limits are given, however, by the requirement for maximum photosensitivity, i.e., for the biggest possible portion of charge transporting compound, and for crystallization to be prevented, i.e.-, for the biggest 'possibleportion of binder. A mixing ratio of about 1 2 1 parts by weight has proved preferable, but mixing ratios from about 3 1 to 1 4 or above, depending on the particular case, are also suitable.

The conventional sensitizers to be used additionally may advantageously foster charge transport. moreover, Moreover, may produce charge carriers in the transparent top layers. Suitable sensitizers are, for example, Rhodamine B extra, Schultz, Farbstofftabellen (dyestuff tables), 1st volume, 7th edition, 1931, No. 864, page 365, Brilliant Green, No. 760, page 314, Crystal Violet, No. 785, page 329,Victoria Pure Blue, No. 822, page 347, and Cryptocyanine, No. 927, page 397. In the same sense as act the sensitizers may also act added compounds which form charge transfer complexes with the charge transporting compound. Thus, it is possible to achieve another increase of the photosensitivity of the described double layers. The quantity of added sensitizer or of the compound forming the charge transfer complex is so determined that the resulting donor acceptor complex with its charge transfer band still is sufficiently transparent to the light absorbed by the organic dyestuff layer below. Compounds which may be used as electron acceptors are, for example: 3,5- and 3,4-dinitro-benzoic acid, tetrachlorophthalic acid anhydride, 2,4,7-trinitrofluorenone, 3,6-dinitro-naphthalic acid anhydride, and N-substituted imides of 3,6-dinitro-naphthalic acid, such as the N-t-butyl-3,6-dinitro-naphthalic acid imide. Optimum concentration is at a molar donor/acceptor ratio of about 10 1 to about 100 2 l and vice versa.

The addition of adhesive as binders to thecharge transporting compounds already yields a good photosensitivity. In this case, low-molecular polyester resin,

such as Adhesive 49,000, Du Pont, has proved particularly suitable.

In the described manner, the top layers have the property to render possible a high charge with a small dark discharge. Whereas in all conventional sensitizations an increase of the photosensitivity is connected with an increase of the dark current, the arrangement of the invention can prevent this parallelity. The layers are thus usable in electrophotograhic copying devices with low copying speeds and very small lamp energies as well as in those with high copying speeds and correspondingly high lamp energies.

The invention will now be described more in detail by reference to the examples the values ofwhich are compiled in the table.

For the preparation of the photoconductive double layers, the dyestuffs listed below are vapor-deposited at a reduced pressure of 10* to 10 mm Hg in a vacuum evaporator (type A-l, marketed by Pfeiffer, Wetzler, Germany) for the periods stated in the table and at the temperatures indicated which are measured directly at the substance to be vapor-deposited on a 90 pm thick aluminum foil mounted at a-distance of. approximeasured extinction at 505 nm of 0.28 and 1.85, re-,

spectively, and assuming an extinction coefficient of e 1.0 10 and a dyestuff density of d I layer thicknesses of 0.18 and 1.1 82 m, respectively, are calculated for the dyestuffs of Formulae l and 2 according to the following equation:

Layer thickness (urn) 10 e M d wherein E is the measured extinction,

e is the extinction coefficient,

M is the molecular weight, and

d is the density of the dyestuff.

When the layers produced for measuring the thickness were used for measuring the sensitivity of the dyestuff towards the light of a xenon lamp having a lightintensity of 487.5 ;1.W/cm the half time of the light decay was found to be, respectively, 46 and 40 msec., and the charge was 810 and -560 volts, respectively, when the dyestuff layers were coated 6 pm thick top layers (To), as described further down.

In order to test the electrophotographic properties of the dyestuff layers thus produced, transparent top layers of 5 to 6 pm thickness are applied to them. For this purpose, 20% tetrahydrofurane solutions of a. 1 part by weight of 2,4,7-trinitrofluorenone and 1 part by weight of a polyester resin, (e.g. Dynapol L 206, a product of Dynamit Nobel, Troisdorf, Germany) (TNF), or

b. 1 part by weight of 2,5-bis-(4-diethylaminophenyl )oxadiazole-1,3,4 and 1 part by weight of a styrene/maleic acid anhydride copolymer (e.g. Lytron 820, a product of Monsanto Corp., USA) (T0), or

c. 1 part by weight of N-t-butyl-3,6-dinitronaphtha1ic acid imide and 1 part by weight of a polyester resin (e.g. Dynapol L 206) (DNl) to which, in some cases, sensitizers are added in. the

than can be achieved by the layers of the present invention.

In order to measure its photosensitivity, each photoconductor layer to be tested is charged to a positive or negative potential by passing it three times through a charging device (e.g. an apparatus of type AG 56, marketed by KALLE AKTlENGESELLSCl-IAFT, WiesbadenBiebrich, Germany) adjusted to 7.5 kV. Subse.-

9 quently, the layer is exposed; to'the lig'ht of'ia xenon lamp (type XBO 1500f Osram)l ln all-cases, the lightintensity in the plane of measurement is approximately 270 aw/em The height of the charge :(V) and the and in which the transparent top layer is composed of a mixture of a binder with a charge transporting, monomeric, heterocyclic compound substi'tuted'by at least one dialkyl-amino group'or two'alkoxy groups and havphoto-induced light deca y curve of the photoconductor layer are measured by an electrometer (type 610 B, marketed by Keithley lnstruments, USA) through a probe by the method described by Arneth and Lorenz in Reprographie 3, 199 (1963). The photoconductor layer'is' characterized by the height of its charge (V) 10 and by the time (T' l/2) after which the charge has dropped to half its original value (V/2).

The following abbreviations areused for the different sensitizers:

RhB-Rhodamine B extra BGBrilliant Green.

" ing an extended rr-electron system,

which recording material is useful in an electroph'otographic copyingprocess with negative charging of the toplayer if an electron-donating compound is used, and is usefulin an electrophot ographic copying process with positive charging of the top layer if the top layer contains an electron-accepting compound. 2. Electrophotographic material according to claim 1 in which the transparent top layer, which is a mixture 15 of a binder and 2,4,7-trinitrofluorenone or 2,5-bis-(4- diethylaminophenyl )-oxadiazole l ,3 ,4, additionally Table No. Formula Vapor Top Sensi- Photosensitivity of Deposition llayefi tizer Dye- T V2 V stuff min/"C (msec) 0 To 2100 420 O TNF l 1000 500 l 1 4/300 TNF 135 690 2 l 2/300 TNF 0.3 RhB 155 1200 3 1 2/300 DNl 0.3 RhB 130 1400 4 1 2/300 To 57 600 S l 4/300 To 0.15 130 32 1300 6 1 4/300 To 0.3 RhB 23 1150 7 2 2/320 TNF 0.3 RhB 59 450 8 2 4/320 To 65 730 9 3 2/310 TNF 0.3 RhB 170 650 10 4 3/310 To 135 620 l l 12 5/360 TNF 380 940 12 14 4/330 TNF 0.3 RhB 120 1450 13 15 4/280 TNF 78 500 l4 15 4/280 TNF 0.3 RhB 58 480 15 15 4/280 To 0.3 RhB 63 1100 16 16 4/330 TNF 82 +520 l7 16 4/330 To 0.3 RhB 76 1100 18 16 4/330 To 0.0 B0 76 +940 19 2 4/320 330 It will be obvious to those skilled in the art that many 40 contains a sensitizer and is combined with a thin vacumodifications may be made within the scope of the present invention without departing from the spirit thereof, and the invention includes all such modifications.

What is claimed is:

1. Electrophotographic recording material comprising an electroconductive support material and a photoconductive double layer of organic materials composed of a tightly packed, homogeneous, uniform, opaque charge carrier producing dyestuff layer and a transparent top layer of insulating materials containing at least one charge transporting compound, in which the organic dyestuff layer is composed of a compound of the general formula NH-CO-CH-N=NA-N=NCHCONH R CO CO R 1 1 2 CH CH wherein 7. Electrophotographic material according to claim A is a diphenyl, 2-phenyl-benzimidazole or azobenzene group which may be substituted, and

R, R R and R may be the same or different and are hydrogen, alkyl with one to four carbon atoms, a1koxy with one to four carbon atoms, or halogen,

um-evaporated dyestuff layer.

3. Electrophotographic material according to claim 1 in which A'-- is substituted by alkyl with one to four carbon atoms, alkoxyl with one to four carbon atoms, and/or halogen.

4. Electrophotographic material according to claim 1 in which methyl, and/or methoxy groups and/or chlorine are present as substituents.

5. Electrophotographic material according to claim 1 in which the organic dyestuff layer consists of Pigment Yellow 12 (Cl. 21,090).

6. Electrophotographic material according to claim 1 in which the organic dyestuff layer consists of Pigment Orange 16 (Cl 21,160).

bis-azo-( 2 ,5-dichloro-2 methoxy-S -methylazobenzene)-bis-(B-acetoacetani1ide).

1 in which the organic dyestuff layer consists of 4,4-

bis-azo-( 2,5-dichloro- ,2 -dimethoxy-azobenzene )-bis- (B-acetoacetanilide 9. Electrophotographic material according to claim 1 in which the organic dyestuff layer has a thickness of about 0.005 to 2 pm and the transparent top layer has a thickness of m. 5 to uum.

10. Electrophotographic material according to claim 1 in which the transparent top layer consists of a 1:1 mixture (by weight) of said charge transporting heterocyclic compound and a binder.

l 1. Electrophotographic material according to claim 1 in which said charge transporting heterocyclic compound is a monomer.

12. Electrophotographic material according to claim 1 in which said 'charge transparting heterocyclic compound is an electron donor compound.

13. Electrophotographic material according to claim 1 in which said heterocyclic compound is selected from the group consisting of oxazoles, oxadiazoles, triazoles, imidazoles and pyrazoles.

l4. Electrophotographic material according to claim 1 in which said heterocyclic compound is an oxadiazole.

15. Electrophotographic material according to claim 1 in which the transparent top layer contains 2,5-bis- (4-diethylaminophenyl)-oxadiazole-1,3,4 as the charge transporting compound.

16. Electrophotographic material according to claim 1 in which the binder is selected from the group consisting of polyesters, copolyesters, silicone resins, copolymers of styrene and maleic acid anhydride, and polycarbonate resins.

17. Electrophotographic material according to claim 1 in which the binder is a copolymer of styrene and maleic acid anydride.

l8. Electrophotographic material according to claim 1 in which an insulating intermediate layer is disposed between the support and the photoconductive double layer.

19. Electrophotographic material according to claim 1 in which the electroconductive support is an aluminum, tin or lead foil or a plastic film provided with an aluminum, tin or lead layer by vapor deposition or lamination. 

1. ELECTROPHOTOGRAPHIC RECORDING MATERIAL COMPRISING AN ELECTROCONDUCTIVE SUPPORT MATERIAL AND A PHOTOCONDUCTIVE DOUBLE LAYER OF ORGANIC MATERIALS COMPOSED OF A TIGHTLY PACKED, HOMOGRNEOUS, UNIFORM, OPAQUE CHARGE CARRIER PRODUCING DYESTUFF LAYER AND A TRANSPARENT TOP LAYER OF INSULATING MATERIALS CONTAINING AT LEAST ONE CHARGE TRANSPORTING COMPOUND, IN WHICH THE ORGANIC DYESTUFF LAYER IS COMPOSED OF COMPOUND OF THE GENERAL FORMULA ((R1,R2-PHENYL)-NH-CO-CH(-CO-CH3)-N=N-)2-A WHEREIN -A- IS A DIPHENYL, 2- PHENYL-BENZIMIDAZOLE OR AZOBENZENE GROUP WHICH MAY BE SUBSTITUTED, AND R, R1, R2 AND R3 MAY BE THE SAME OR DIFFERENT AND ARE HYDROGEN, ALKYL WITH ONE TO FOUR CARBON ATOMS, ALKOXY WITH ONE TO FOUR CARBON ATOMS, OR HALOGEN, AND IN WHICH THE TRANSPARENT TOP LAYER IS COMPOSED OF A MIXTURE OF A BINDER WITH A CHARGE TRANSPORTING, MONOMERIC, HETEROCYCLIC COMPOUND SUBSTITUTED BY AT LEAST ONE DIALKYL-AMINO GROUP OR TWO ALKOXY GROUPS AND HAVING AN EXTENDED $ELECTRON SYSTEM, WHICH RECORDING MATERIAL IS USEFUL IN AN ELECTROPHOTOGRAHIC COPYING PROCESS WITH NEGATIVE CHARGING OF THE TOP LAYER IF AN ELECTRON-DONATING COMPOUND IS USED, AND IS USEFUL IN AN ELECTROPHOTOGRAPHIC COPYING PROCESS WITH POSITIVE CHARGING OF THE TOP LAYER IF THE TOP LAYER CONTAINS AN ELECTRON-ACCEPTING COMPOUND.
 2. Electrophotographic material according to claim 1 in which the transparent top layer, which is a mixture of a binder and 2, 4,7-trinitrofluorenone or 2,5-bis-(4-diethylaminophenyl)-oxadiazole-1,3,4, additionally contains a sensitizer and is combined with a thin vacuum-evaporated dyestuff layer.
 3. Electrophotographic material according to claim 1 in which -A- is substituted by alkyl with one to four carbon atoms, alkoxyl with one to four carbon atoms, and/or halogen.
 4. Electrophotographic material according to claim 1 in which methyl, and/or methoxy groups and/or chlorine are present as substituents.
 5. Electrophotographic material according to claim 1 in which the organic dyestuff layer consists of Pigment Yellow 12 (C.I. 21,090).
 6. Electrophotographic material according to claim 1 in which the organic dyestuff layer consists of Pigment Orange 16 (C.I 21, 160).
 7. Electrophotographic material according to claim 1 in which the organic dyestuff layer consists of 4,4''-bis-azo-(2,5-dichloro-2''-methoxy-5''-methyl-azobenzene)-bis-( Beta -acetoacetanilide).
 8. Electrophotographic material according to claim 1 in which the organic dyestuff layer consists of 4,4''-bis-azo-(2,5-dichloro-5,2''-dimethoxy-azobenzene)-bis-( Beta -acetoacetanilide).
 9. Electrophotographic material according to claim 1 in which the organic dyestuff layer has a thickness of about 0.005 to 2 Mu m and the transparent top layer has a thickness of m. 5 to 20 Mu um.
 10. Electrophotographic material according to claim 1 in which the transparent top layer consists of a 1:1 mixture (by weight) of said charge transporting heterocyclic compound and a binder.
 11. Electrophotographic material according to claim 1 in which said charge transporting heterocyclic compound is a monomer.
 12. Electrophotographic material according to claim 1 in which said charge transparting heterocyclic compound is an electron donor compound.
 13. Electrophotographic material according to claim 1 in which said heterocyclic compound is selected from the group consisting of oxazoles, oxadiazoles, triazoles, imidazoles and pyrazoles.
 14. Electrophotographic material according to claim 1 in which said heterocyclic compound is an oxadiazoLe.
 15. Electrophotographic material according to claim 1 in which the transparent top layer contains 2,5-bis-(4-diethylaminophenyl)-oxadiazole-1,3,4 as the charge transporting compound.
 16. Electrophotographic material according to claim 1 in which the binder is selected from the group consisting of polyesters, copolyesters, silicone resins, copolymers of styrene and maleic acid anhydride, and polycarbonate resins.
 17. Electrophotographic material according to claim 1 in which the binder is a copolymer of styrene and maleic acid anydride.
 18. Electrophotographic material according to claim 1 in which an insulating intermediate layer is disposed between the support and the photoconductive double layer.
 19. Electrophotographic material according to claim 1 in which the electroconductive support is an aluminum, tin or lead foil or a plastic film provided with an aluminum, tin or lead layer by vapor deposition or lamination. 